Sheet conveyance apparatus

ABSTRACT

A sheet conveyance apparatus includes a conveyance roller, an abutment member including an abutment surface, an obliquely conveying roller configured to convey the sheet such that the side edge portion is moved toward the abutment surface, a sheet side-edge detection portion, and a controller. The controller is configured to control the conveyance force of the obliquely conveying roller at a first conveyance force until a predetermined time has elapsed, in an abutment operation in which the sheet is abutted against the abutment surface by the obliquely conveying roller, and control the conveyance force of the obliquely conveying roller at a second conveyance force larger than the first conveyance force if the predetermined time has elapsed and the position of the side edge portion of the sheet detected by the sheet side-edge detection portion is out of a predetermined range.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a sheet conveyance apparatus thatconveys sheets.

Description of the Related Art

Japanese Patent Application Publication No. H11-189355 proposes an imageforming apparatus that includes a feeding portion that feeds a sheet, asheet alignment portion that corrects the posture of a sheet that isbeing conveyed, and a registration portion that sends a sheet whoseposture has been corrected in the sheet alignment portion, at apredetermined timing. The image forming apparatus also includes an imagetransfer portion that transfers an image onto a sheet sent by theregistration portion, and a fixing portion that fixes the image havingbeen transferred onto the sheet by the image transfer portion, to thesheet.

The sheet alignment portion includes obliquely conveying rollers,conveyance rollers, a sheet-passage detection sensor, and a sheetside-edge detection sensor. The obliquely conveying rollers convey asheet toward a reference guide; the conveyance rollers move a sheet in awidth direction orthogonal to a sheet conveyance direction; and thesheet side-edge detection sensor detects the position of a side edge ofa sheet. The obliquely conveying rollers convey a sheet such that thesheet is aligned with the reference guide, and thereby corrects the skewof the sheet. The conveyance rollers move a sheet in the widthdirection, depending on a detection signal from the sheet side-edgedetection sensor, to a position at which the side edge of the sheet isnot detected by the sheet side-edge detection sensor.

The sheet alignment portion described in Japanese Patent ApplicationPublication No. H11-189355 is a sheet conveyance apparatus that causesthe obliquely conveying rollers to convey a sheet such that the sheet isaligned with the reference guide. In such a sheet conveyance apparatus,after the sheet abuts against the reference guide, the sheet is conveyedwhile the obliquely conveying rollers slip on the sheet. Thus, such asheet conveyance apparatus is easily affected by the conveyanceresistance of the sheet when the sheet is conveyed by the obliquelyconveying rollers. If the sheet has a large conveyance resistance, theconveyance of the sheet performed by the obliquely conveying rollers maybe delayed. If the conveyance of the sheet is delayed, the sheet willnot reach a roller (located downstream of the obliquely conveyingrollers) in a predetermined time, decreasing the productivity.

SUMMARY OF THE INVENTION

According to one aspect to the present invention, a sheet conveyanceapparatus includes a conveyance roller configured to convey a sheet, anabutment member including an abutment surface and configured to correctskew of the sheet, the abutment surface being disposed downstream of theconveyance roller and extending along a sheet conveyance direction, theabutment surface being a surface against which a side edge portion ofthe sheet in a width direction orthogonal to the sheet conveyancedirection abuts, an obliquely conveying roller disposed downstream ofthe conveyance roller in the sheet conveyance direction and configuredto convey the sheet such that the side edge portion is moved toward theabutment surface, a sheet side-edge detection portion configured todetect a position of the side edge portion of the sheet in the widthdirection and change an output value in accordance with the position ofthe side edge portion of the sheet conveyed by the obliquely conveyingroller, and a controller configured to control conveyance force appliedby the obliquely conveying roller in the width direction of the sheet,in accordance with a detection result from the sheet side-edge detectionportion. The controller is configured to control the conveyance force ofthe obliquely conveying roller at a first conveyance force until apredetermined time has elapsed, in an abutment operation in which thesheet is abutted against the abutment surface by the obliquely conveyingroller, and control the conveyance force of the obliquely conveyingroller at a second conveyance force larger than the first conveyanceforce if the predetermined time has elapsed and the position of the sideedge portion of the sheet detected by the sheet side-edge detectionportion is out of a predetermined range.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a printer of a first embodiment.

FIG. 2 is a schematic diagram illustrating a registration unit of thefirst embodiment.

FIG. 3 is a block diagram illustrating control blocks of the firstembodiment.

FIG. 4 is a flowchart illustrating an abutment operation performed bythe registration unit of the first embodiment.

FIG. 5 is a diagram illustrating conveyance of a sheet performed by aconveyance roller portion of the first embodiment.

FIG. 6 is a diagram illustrating conveyance of a sheet performed by anobliquely-conveying roller portion of the first embodiment.

FIG. 7 is a diagram illustrating a case in which normal control isperformed in the registration unit of the first embodiment.

FIG. 8 is a diagram illustrating a state in which the abutment operationhas been completed in the registration unit of the first embodiment.

FIG. 9 is a diagram illustrating a case in which recovery control isperformed in the registration unit of the first embodiment.

FIG. 10 is a diagram illustrating conveyance of a sheet performed by aregistration roller pair in the registration unit of the firstembodiment.

FIG. 11 is a graph illustrating the output value from a CIS that changeswith time, and that is obtained in a case where the normal control isperformed in the registration unit of the first embodiment.

FIG. 12 is a graph illustrating the output value from the CIS thatchanges with time, and that is obtained in a case where the recoverycontrol is performed in the registration unit of the first embodiment.

FIG. 13 is a flowchart illustrating an abutment operation performed by aregistration unit of a second embodiment.

FIG. 14 is a flowchart illustrating an abutment operation performed by aregistration unit of a third embodiment.

DESCRIPTION OF THE EMBODIMENTS First Embodiment Overall Configuration

First, an embodiment of the present invention will be described.Full-color image forming apparatuses are classified into a tandem systemand a rotary system. In the tandem system, a plurality of processcartridges is arranged side by side; in the rotary system, a pluralityof process cartridges is arranged cylindrically. In addition, the imageforming apparatuses are classified, regarding the transfer system, intoa direct transfer system and an intermediate transfer system. In thedirect transfer system, a toner image is directly transferred from aphotosensitive member onto a sheet; in the intermediate transfer system,a toner image is temporarily transferred onto an intermediate transferbelt and then transferred from the intermediate transfer belt onto asheet. Image forming apparatuses classified as the intermediate transfersystem eliminate the need of holding a sheet on a transfer drum, andthus can form images on a variety of types of sheets, such as thickpaper sheets and coated sheets. In addition, the image formingapparatuses classified as the intermediate transfer system enable theplurality of process cartridges to perform parallel processing, andtransfer a full-color image at a time. Thus, the image formingapparatuses classified as the intermediate transfer system are suitablefor achieving high productivity.

As illustrated in FIG. 1 , a printer 1 that serves as an image formingapparatus of a first embodiment is an electrophotographic full-colorlaser-beam printer classified as the tandem-type intermediate-transfersystem. The printer 1 includes a feeding unit 13, a conveyance unit 141,a registration unit 144, an image forming unit 11, a fixing unit 12, anda branch-and-conveyance unit 146. The printer 1 further includes areverse conveyance unit 147, a duplex conveyance unit 149, a dischargingtray 148, and an escape tray 152.

The image forming unit 11 includes four process cartridges 10Y, 10M,10C, and 10Bk. The four process cartridges are used for forming fourtoner images of yellow (Y), magenta (M), cyan (C), and black (Bk). Inaddition, the image forming unit 11 includes exposure apparatuses 104 a,104 b, 104 c, and 104 d. Note that the four process cartridges 10Y, 10M,10C, and 10Bk are the same as each other, except that they producedifferent colors of image. For this reason, the configuration and theimage forming process of only the process cartridge 10Y will bedescribed, and the description for the process cartridges 10M, 10C, and10Bk will be omitted.

The process cartridge 10Y includes a photosensitive drum 101 a, acharging roller, a development unit 102 a, and a cleaner 103 a. Thephotosensitive drum 101 a has an organic photoconductive layer formed onthe outer surface of an aluminum cylinder, and is rotated by a drivingmotor toward a direction indicated by an arrow A. The image forming unit11 also includes an intermediate transfer belt 111 that is rotated by adriving roller 115 toward a direction indicated by an arrow B. Theintermediate transfer belt 111 is wound around a tension roller 116, thedriving roller 115, and a secondary transfer inner roller 113. Insidethe intermediate transfer belt 111, primary transfer rollers 112 a, 112b, 112 c, and 112 d are disposed; outside the intermediate transfer belt111, a secondary transfer outer roller 118 is disposed, facing thesecondary transfer inner roller 113.

The fixing unit 12 includes a fixing roller pair 12 a, and a pre-fixingconveyance portion 145 that conveys a sheet to a nip of the fixingroller pair 12 a. The feeding unit 13 includes a lift plate 131 and anair feeding portion 132. The lift plate 131 moves up and down in a statewhere a sheet S is stacked on the lift plate 131, and the air feedingportion 132 feeds the sheet S stacked on the lift plate 131. The airfeeding portion 132 separates one sheet from the other stacked on thelift plate 131 by using air; and conveys the uppermost sheet stacked onthe lift plate 131, while causing the uppermost sheet to stick to theair feeding portion 132 by using air. Note that another feeding portion,such as a roller or a belt, may be used instead of the air feedingportion 132.

Next, an image forming operation of the printer 1 configured in thismanner will be described. When an image signal is sent to the exposureapparatus 104 a from an apparatus, such as a personal computer, a laserbeam generated in accordance with the image signal is emitted from theexposure apparatus 104 a to the photosensitive drum 101 a of the processcartridge 10Y, and the photosensitive drum 101 a is irradiated with thelaser beam.

Since the surface of the photosensitive drum 101 a is uniformly chargedin advance by the charging roller so as to have a predetermined polarityand potential, an electrostatic latent image is formed on the surface ofthe photosensitive drum 101 a when the surface is irradiated with thelaser beam emitted from the exposure apparatus 104 a to thephotosensitive drum 101 a via a mirror 105 a. The electrostatic latentimage formed on the photosensitive drum 101 a is developed by thedevelopment unit 102 a, and a yellow (Y) toner image is formed on thephotosensitive drum 101 a.

Similarly, photosensitive drums of the process cartridges 10M, 10C, and10Bk are also irradiated with laser beams emitted from the exposureapparatuses 104 b, 104 c, and 104 d; and magenta (M), cyan (C), andblack (Bk) toner images are formed on the photosensitive drums. Thetoner images formed on the photosensitive drums are transferred onto theintermediate transfer belt 111 by the primary transfer rollers 112 a,112 b, 112 c, and 112 d. Then the full-color toner image is conveyed toa secondary transfer nip T2 formed by the secondary transfer innerroller 113 and the secondary transfer outer roller 118, by theintermediate transfer belt 111 rotated by the driving roller 115. Thetoner left on the photosensitive drum 101 a is collected by the cleaner103 a. Note that the image forming process for each color is performedat a timing at which a corresponding toner image is transferred ontoanother toner image which has been primary-transferred onto theintermediate transfer belt 111 at a position located upstream of theposition at which the corresponding toner image is transferred.

In parallel with the above-described image forming process, the sheet Sis fed from the feeding unit 13 in the printer 1. The sheet S isconveyed to the registration unit 144 by the conveyance unit 141 in asheet conveyance direction indicated by an arrow C (hereinafter, thesheet conveyance direction is indicated by the arrow C). Theregistration unit 144 corrects the skew of the sheet S, and conveys thesheet S to the secondary transfer nip T2, which serves as an imageforming portion, at a predetermined conveyance timing. Then a full-colortoner image on the intermediate transfer belt 111 is transferred onto afirst sheet surface (front surface) of the sheet S by a secondarytransfer bias applied to the secondary transfer outer roller 118. Theresidual toner left on the intermediate transfer belt 111 is collectedby a belt cleaner 114.

The sheet S onto which the toner image has been transferred is conveyedto the fixing roller pair 12 a by the pre-fixing conveyance portion 145.The sheet S is then applied with predetermined heat and pressure by thefixing roller pair 12 a, and thereby the toner is melted and solidified(fixed). The sheet S having passed through the fixing unit 12 isconveyed to the branch-and-conveyance unit 146, and thebranch-and-conveyance unit 146 selects a path of the sheet S from afirst discharging path 150 a and a second discharging path 150 b.

In a case where an image is formed on only one side of the sheet S, thesheet S is conveyed from the branch-and-conveyance unit 146 to the firstdischarging path 150 a, and is discharged to the discharging tray 148that serves as a first tray.

In a case where images are formed on both sides of the sheet S, thesheet S is conveyed to the second discharging path 150 b by thebranch-and-conveyance unit 146. The sheet S having been conveyed to thesecond discharging path 150 b is conveyed to a guide member 151, and theguide member 151 selects a path of the sheet S from an escape path 151 aand a reversing path 151 b. The sheet S having been guided to the escapepath 151 a by the guide member 151 is discharged to the escape tray 152that serves as a second tray. For example, if the sheet S cannot be usedas a product due to image defect or the like, the sheet S is dischargedto the escape tray 152.

The sheet S having been conveyed to the reversing path 151 b is conveyedto the reverse conveyance unit 147, and is switch-backed by the reverseconveyance unit 147. The sheet S having been switch-backed is conveyedfrom the reverse conveyance unit 147 to the duplex conveyance unit 149,and is guided to the conveyance unit 141. After that, an image is formedon a second sheet surface (back surface) of the sheet S in the secondarytransfer nip T2, and the sheet S is discharged to the discharging tray148.

Registration Unit

Next, the registration unit 144 will be described with reference to FIG.2 . The registration unit 144 includes a conveyance roller portion 201,an obliquely-conveying roller portion 205, a registration roller pair207, a reference member 204 that serves as an abutment member, a CIS202, a conveyance sensor 203, and a pre-registration sensor 206. The CIS202 is a contact image sensor.

The conveyance roller portion 201 serves as a conveyance roller and afirst conveyance roller, and includes a plurality of (three in the firstembodiment) conveyance roller pairs 201 a, 201 b, and 201 c. Theconveyance roller pairs 201 a to 201 c are disposed side by side in thesheet conveyance direction C, and have an identical configuration. Forexample, the conveyance roller pair 201 a includes a rotary shaft 211 a,a driving roller 212 a, and a driven roller 213 a (see FIG. 1 ). Therotary shaft 211 a extends in a width direction W, and serves as a firstrotary shaft. The driving roller 212 a is rotatably supported by therotary shaft 211 a, and serves as a first rotary member. The drivenroller 213 a faces the driving roller 212 a. The width direction W is anaxial direction, and is orthogonal to the sheet conveyance direction C.In the conveyance roller pair 201 a, the driven roller 213 a can bebrought into pressure contact with and separated from the driving roller212 a, so that the state of the conveyance roller pair 201 a can beswitched between a nip state in which the sheet S is nipped and a nipcancellation state in which the sheet S is not nipped.

The CIS 202 serves as a sheet side-edge detection portion, and isdisposed between the conveyance roller pair 201 b and the conveyanceroller pair 201 c in the sheet conveyance direction C. In addition, theCIS 202 is disposed on the reference member 204 side in the widthdirection W, with respect to a center line CCP of the conveyance paththrough which the sheet S passes. The CIS 202 detects the position of anedge portion of the sheet S in the width direction W, and changes theoutput value in accordance with the position of the edge portion of thesheet S. Thus, the CIS 202 can measure the relative distance between thesheet S and the reference member 204, regardless of variations ofcutting processes performed in the paper-sheet width direction. Notethat the arrangement of the CIS 202 is not limited to theabove-described arrangement. In addition, the CIS 202 may not be acontact image sensor. For example, the CIS 202 may be one of varioussensors including contact-type sensors and noncontact-type sensors. Inanother case, a flag sensor or a transmissive or reflective photo sensormay be used instead of the CIS 202.

The conveyance sensor 203 is disposed downstream of the conveyanceroller pair 201 c and upstream of the obliquely-conveying roller pair205 a in the sheet conveyance direction C, and on the center line CCP.The conveyance sensor 203 is a photo sensor that includes a lightemitting portion and a light receiving portion. Thus, the conveyancesensor 203 detects a passage timing of the sheet S by the lightreceiving portion receiving the light emitted by the light emittingportion and reflected by the sheet S.

The reference member 204 is disposed downstream of the conveyance sensor203 in the sheet conveyance direction C. In addition, the referencemember 204 is disposed in a position in which a reference surface 204 athat serves as an abutment surface extends along a side edge portion Sa(see FIG. 5 ) of the sheet S. The side edge portion Sa is an edgeportion of the sheet S in the width direction W.

The obliquely-conveying roller portion 205 is disposed downstream of theconveyance roller portion 201 in the sheet conveyance direction C and inthe vicinity of the reference member 204, and includes a plurality of(three in the first embodiment) obliquely-conveying roller pairs 205 a,205 b, and 205 c. The obliquely-conveying roller pairs 205 a to 205 care disposed side by side in the sheet conveyance direction C, and havean identical configuration. For example, the obliquely-conveying rollerpair 205 a includes a rotary shaft 221 a that serves as a second rotaryshaft. Because the obliquely-conveying roller pair 205 a is inclined byan angle of θ with respect to the reference surface 204 a of thereference member 204 disposed in parallel with the sheet conveyancedirection C, the rotary shaft 221 a extends in a direction that crossesthe sheet conveyance direction C and the width direction W. In addition,the obliquely-conveying roller pair 205 a includes a driving roller 222a that serves as a second rotary member. The driving roller 222 a isrotatably supported by the rotary shaft 221 a, and is driven by anobliquely-conveying driving motor 34 a (see FIG. 3 ). In addition, theobliquely-conveying roller pair 205 a includes a driven roller 223 a(see FIG. 1 ) that faces the driving roller 222 a. In theobliquely-conveying roller pair 205 a, the driven roller 223 a can bebrought into pressure contact with and separated from the driving roller222 a, so that the state of the obliquely-conveying roller pair 205 acan be switched between a nip state in which the sheet S is nipped and anip cancellation state in which the sheet S is not nipped.

Since the rotary shafts are inclined by the angle of θ with respect tothe reference surface 204 a, the obliquely-conveying roller portion 205can apply conveyance force that has a component obtained in the sheetconveyance direction C and a component obtained in the width directionW, in which the sheet S abuts against the reference surface 204 a. Theskew of the sheet S is corrected by the side edge portion of the sheet Sabutting against the reference surface 204 a. The side edge portion ofthe sheet S is an edge portion of the sheet S in the width direction W.

The pre-registration sensor 206 serves as a sheet downstream-edgedetection portion; and is disposed downstream of the obliquely-conveyingroller pair 205 c and upstream of the registration roller pair 207 inthe sheet conveyance direction C, and on the center line CCP. Thepre-registration sensor 206 is a photo sensor that is substantially thesame as the conveyance sensor 203, and detects a passage timing of thesheet S by the light receiving portion receiving the light emitted bythe light emitting portion and reflected by the sheet S.

The registration roller pair 207 includes a driving roller and a drivenroller. The registration roller pair 207 moves in the width direction Wwhile nipping the sheet S; and thereby positions the sheet S in thewidth direction W, in accordance with the position of a toner imageformed on the intermediate transfer belt 111. The registration rollerpair 207 that serves as a second conveyance roller conveys the sheet Safter positioning the sheet S in the width direction W.

Control Block

Next, control blocks of the printer 1 will be described with referenceto FIG. 3 . As illustrated in FIG. 3 , the printer 1 includes acontroller 31 that serves as a controller. The controller 31 includes aCPU 31 a, a ROM 31 b, a RAM 31 c, and a timer 31 d. The CPU 31 a readsvarious programs stored in the ROM 31 b, and controls each portion ofthe printer 1. The RAM 31 c is used as a work area of the CPU 31 a. Thetimer 31 d measures time.

The controller 31 is connected with the CIS 202, the conveyance sensor203, the pre-registration sensor 206, conveyance driving motors 32 a, 32b, and 32 c, and conveyance attachment-and-detachment units 33 a, 33 b,and 33 c. In addition, the controller 31 is connected withobliquely-conveying driving motors 34 a, 34 b, and 34 c,obliquely-conveying attachment-and-detachment units 35 a, 35 b, and 35c, a registration-roller driving motor 36, and a switching motor 37. Thecontroller 31 controls the conveyance force of the obliquely-conveyingroller portion 205, in accordance with a detection result from the CIS202. The control performed by the controller 31 will be morespecifically described below.

The conveyance driving motors 32 a, 32 b, and 32 c respectively drivethe conveyance roller pairs 201 a, 201 b, and 201 c. Each of theconveyance attachment-and-detachment units 33 a, 33 b, and 33 c servesas a conveyance-rollers-nip switching unit. Specifically, the conveyanceattachment-and-detachment unit 33 a moves one or both rollers of theconveyance roller pair 201 a in a direction in which both of the rollersabut against or are separated from each other. Similarly, the conveyanceattachment-and-detachment unit 33 b moves one or both rollers of theconveyance roller pair 201 b in a direction in which both of the rollersabut against or are separated from each other, and the conveyanceattachment-and-detachment unit 33 c moves one or both rollers of theconveyance roller pair 201 c in a direction in which both of the rollersabut against or are separated from each other. In the registration unit144 of the first embodiment, the driven rollers of the conveyance rollerpairs 201 a, 201 b, and 201 c are brought into contact with andseparated from the respective driving rollers.

The obliquely-conveying driving motors 34 a, 34 b, and 34 c respectivelydrive the obliquely-conveying roller pairs 205 a, 205 b, and 205 c. Eachof the obliquely-conveying attachment-and-detachment unit 35 a, 35 b,and 35 c serves as an obliquely-conveying-rollers-nip switching unit.Specifically, the obliquely-conveying attachment-and-detachment unit 35a moves one or both rollers of the obliquely-conveying roller pair 205 ain a direction in which both of the rollers abut against or areseparated from each other. Similarly, the obliquely-conveyingattachment-and-detachment unit 35 b moves one or both rollers of theobliquely-conveying roller pair 205 b in a direction in which both ofthe rollers abut against or are separated from each other, and theconveyance attachment-and-detachment unit 35 c moves one or both rollersof the obliquely-conveying roller pair 205 c in a direction in whichboth of the rollers abut against or are separated from each other. Inthe registration unit 144 of the present embodiment, the driven rollersof the obliquely-conveying roller pairs 205 a, 205 b, and 205 c arebrought into contact with and separated from the respective drivingrollers.

The registration-roller driving motor 36 drives the registration rollerpair 207. The switching motor 37 swings the guide member 151, so thatthe conveyance path of the sheet S is switched between the escape path151 a and the reversing path 151 b.

Abutment Operation of Sheet

Next, with reference to a flowchart of FIG. 4 , an abutment operation ofthe registration unit 144 of the first embodiment, in which the sheet Sis abutted against the reference surface 204 a, will be described. Inthe abutment operation, the sheet S is conveyed by theobliquely-conveying roller portion 205, so that the side edge portion Sa(see FIG. 5 ) of the sheet S abuts against the reference surface 204 a.

First, as illustrated in FIG. 4 , the controller 31 switches the stateof the obliquely-conveying roller portion 205 to a non-nip state (S1).In this process, the controller 31 causes the obliquely-conveyingattachment-and-detachment units 35 a to 35 c to switch the state of theobliquely-conveying roller portion 205 to the non-nip state, and therebycauses the obliquely-conveying roller portion 205 to stand by in a statewhere the nip of the obliquely-conveying roller portion 205 is released.Then the controller 31 switches the state of the conveyance rollerportion 201 to a nip state (S2). In this process, the controller 31causes the conveyance attachment-and-detachment units 33 a to 33 c toswitch the state of the conveyance roller portion 201 to the nip state,and thereby causes the conveyance roller portion 201 to stand by in astate where the nip of the conveyance roller portion 201 is formed.

Then the controller 31 causes the conveyance roller portion 201 to startto convey the sheet S (S3). In this process, as illustrated in FIG. 5 ,the controller 31 causes the conveyance driving motors 32 a to 32 c todrive the conveyance roller pairs 201 a to 201 c in the nip state, forconveying the sheet S.

Then the controller 31 determines whether a predetermined time α haselapsed since the conveyance sensor 203 detected a leading edge Sb ofthe sheet S that is an edge portion of the sheet S on the downstreamside in the sheet conveyance direction C (S4). As illustrated in FIG. 6, in the registration unit 144, when the predetermined time α haselapsed since the conveyance sensor 203 detected the leading edge Sb ofthe sheet S, the sheet S reaches the obliquely-conveying roller pair 205a. The controller 31 causes the timer 31 d to start to measure time whenthe conveyance sensor 203 detects the leading edge Sb of the sheet S. Ifthe controller 31 determines that the predetermined time α has notelapsed (S4 No), then the controller 31 returns to Step S3. Then thecontroller 31 repeats the steps S3 and S4 and causes the conveyanceroller portion 201 to continue to convey the sheet S until thepredetermined time α has elapsed.

If the controller 31 determines that the predetermined time α haselapsed since the conveyance sensor 203 detected the leading edge Sb ofthe sheet S (S4 Yes), then the controller 31 determines that the sheet Shas been conveyed to the obliquely-conveying roller portion 205 by theconveyance roller portion 201. Then the controller 31 causes theobliquely-conveying attachment-and-detachment units 35 a to 35 c toswitch the state of the obliquely-conveying roller portion 205 to thenip state (S5). After that, since the controller 31 is to cause theobliquely-conveying roller portion 205 to start to convey the sheet S,the controller 31 causes the conveyance attachment-and-detachment units33 a to 33 c to switch the state of the conveyance roller portion 201 tothe non-nip state (S6). Then the controller 31 causes theobliquely-conveying roller portion 205 to convey the sheet S, by drivingthe obliquely-conveying driving motors 34 a to 34 c (S7).

In the registration unit 144, in the steps S5 to S7, the obliqueconveyance of the sheet S is started by the obliquely-conveying rollerportion 205, and the skew of the sheet S and the position of the sheet Sin the width direction W are corrected as the sheet is conveyedobliquely. In addition, in the steps S5 and S7, the controller 31controls the obliquely-conveying roller portion 205 so that therotational speed and the nip pressure of the obliquely-conveying rollerportion 205 are controlled at a first rotational speed and a firstpressure, which are preset for each type of the sheet S. In this manner,the controller 31 controls the conveyance force of theobliquely-conveying roller portion 205 at a first conveyance force, andcauses the obliquely-conveying roller portion 205 to convey the sheet S.

Then the controller 31 determines whether a predetermined time β haselapsed since the conveyance sensor 203 detected the leading edge Sb ofthe sheet S (S8). If the controller 31 determines, in this process, thatthe predetermined time β has not elapsed since the conveyance sensor 203detected the leading edge Sb of the sheet S (S8 No), then the controller31 repeats Step S8 and causes the obliquely-conveying roller portion 205to continue to convey the sheet S until the predetermined time β haselapsed.

On the other hand, if the controller 31 determines that thepredetermined time β has elapsed since the conveyance sensor 203detected the leading edge Sb of the sheet S (S8 Yes), then thecontroller 31 determines whether the position of the side edge portionSa of the sheet S detected by the CIS 202 is within a predeterminedrange L at the position of the CIS 202 (S9).

FIG. 7 illustrates a case in which the position of the side edge portionSa of the sheet S is within the predetermined range L, in Step S9, atthe position of the CIS 202. For example, the predetermined range Lillustrated in FIG. 7 is ±0.3 mm with respect to the position of thereference surface 204 a in the width direction W. If the predeterminedtime β has elapsed since the conveyance sensor 203 detected the leadingedge Sb of the sheet S, and the position of the side edge portion Sa ofthe sheet S is within the predetermined range L determined with respectto the reference surface 204 a, the controller 31 determines that thesheet S has a small conveyance resistance and is being conveyed withoutdelay. In this case, the controller 31 does not change the rotationalspeed of the obliquely-conveying roller portion 205; and executes normalcontrol under which the conveyance force of the obliquely-conveyingroller portion 205, which is set in Step S7, is kept.

FIG. 8 is a diagram illustrating a case in which the abutment operationis continued in a state where the conveyance force of theobliquely-conveying roller portion 205, which is set in Step S7, iskept. As illustrated in FIG. 8 , in the registration unit 144, since theconveyance by the obliquely-conveying roller portion 205 is continued,the side edge portion Sa and the reference surface 204 a contact eachother before the leading edge Sb of the sheet S reaches thepre-registration sensor 206. In this manner, the skew of the sheet S andthe position of the sheet S in the width direction W are corrected inthe registration unit 144. After that, in the registration unit 144, thesheet S is conveyed, while the side edge portion Sa of the sheet Sslides on the reference surface 204 a, until the leading edge Sb of thesheet S reaches the registration roller pair 207.

As described above, the controller 31 determines whether the position ofthe side edge portion Sa of the sheet S is within the predeterminedrange L, when the predetermined time β has elapsed, following thepredetermined time α, since the conveyance sensor 203 detected theleading edge Sb of the sheet S. In the registration unit 144, if thesheet S is skewed significantly, the position of the side edge portionSa of the sheet S may be out of the predetermined range L when thepredetermined time β has elapsed, even if the position of the side edgeportion Sa is within the predetermined range L when the predeterminedtime α has elapsed. In such a case, in the registration unit 144, if theabutment operation is continued without changing the conveyance force ofthe obliquely-conveying roller portion 205, the abutment operation maynot be completed before the sheet S reaches the registration roller pair207.

However, in the steps S8, S9 and S10, the controller 31 can prevent sucha case in which the abutment operation is not completed before the sheetS reaches the registration roller pair 207. Thus, the controller 31 cansuppress failure in conveyance of sheets and image defect, which arecaused by the uncompleted abutment operation. The predetermined time βis a predetermined time (first time) of the first embodiment.

If the controller 31 determines in Step S9 that the position of the sideedge portion Sa of the sheet S is not within the predetermined range Lat the position of the CIS 202 (S9 No), then the controller 31determines that the Sheet S has a large conveyance resistance and isbeing conveyed with delay. FIG. 9 illustrates a case in which thecontroller 31 determines in Step S9 that the position of the side edgeportion Sa of the sheet S is not within the predetermined range L (thatis, out of the predetermined range L) at the position of the CIS 202. Insuch a case, since the conveyance delay of the sheet S is not eliminatedeven if the normal control is continued, the controller 31 executesrecovery control and changes the conveyance force of theobliquely-conveying roller portion 205, for eliminating the conveyancedelay. In the recovery control, the controller 31 of the firstembodiment increases the conveyance speed of the sheet S by changing therotational speed of the obliquely-conveying roller portion 205 from thefirst rotational speed to a second rotational speed, by increasing therotational speed of the obliquely-conveying driving motors 34 a to 34 c(S10).

In this manner, the controller 31 changes the conveyance force of theobliquely-conveying roller portion 205 to a second conveyance forcelarger than the first conveyance force, which is set in the steps S5 andS7. As a result, the sheet S can be conveyed downstream in the sheetconveyance direction C, without conveyance delay.

The controller 31 proceeds to Step S11 after Step S10 or if thecontroller 31 determines in Step S9 that the position of the side edgeportion Sa of the sheet S is within the predetermined range L at theposition of the CIS 202 (S9 Yes). In Step S11, the controller 31determines whether a predetermined time γ has elapsed since thepre-registration sensor 206 detected the leading edge Sb of the sheet S(S11). The predetermined time γ is a second time. If the controller 31determines, in this process, that the predetermined time γ has notelapsed since the pre-registration sensor 206 detected the leading edgeSb of the sheet S (S11 No), then the controller 31 repeats Step S11 andcauses the obliquely-conveying roller portion 205 to continue to conveythe sheet S until the predetermined time γ has elapsed.

If the controller 31 determines that the predetermined time γ haselapsed since the pre-registration sensor 206 detected the leading edgeSb of the sheet S (S11 Yes), then the controller 31 determines that thesheet S has been conveyed to the registration roller pair 207 by theobliquely-conveying roller portion 205. Then the controller 31 causesthe registration roller pair 207 to convey the sheet S, by driving theregistration-roller driving motor 36 (S12). After that, the controller31 causes the obliquely-conveying attachment-and-detachment units 35 ato 35 c to switch the state of the obliquely-conveying roller portion205 to the non-nip state (S13), and causes the registration roller pair207 to convey the sheet S to the secondary transfer portion locateddownstream of the registration unit 144 in the sheet conveyancedirection C.

FIG. 10 illustrates a state in which the conveyance of the sheet S isstarted by the registration roller pair 207 in a state where theabutment operation is completed. When the controller 31 causes theregistration roller pair 207 to convey the sheet S in the sheetconveyance direction C, the controller 31 switches the state of theobliquely-conveying roller portion 205 to the non-nip state forpreventing the component of the conveyance force of theobliquely-conveying roller portion 205 obtained in the width directionW, from affecting the conveyance of the sheet S.

Note that in the registration unit 144, if the sheet S is skewedsignificantly and the sheet S has a large conveyance resistance, theposition of the side edge portion Sa of the sheet S may not be withinthe predetermined range L at the position of the CIS 202 before theleading edge Sb of the sheet S reaches the pre-registration sensor 206.In this case, the controller 31 determines that the abutment operationwill not be completed before the leading edge Sb of the sheet S reachesthe registration roller pair 207, and stops the conveyance of the sheetS for preventing image defect, such as misalignment of printing. Inaddition, the controller 31 causes an informing unit (not illustrated)to inform a user that the image defect (misalignment of printing) may beoccurring due to the uncompleted abutment operation, that the conveyanceof the sheet is being stopped, and that the sheet left in the printer 1needs to be removed.

Output Value from CIS

FIG. 11 is a graph illustrating the output value from the CIS 202 thatchanges with time, and that is obtained when the normal control isperformed by the controller 31. The horizontal axis represents the time,and the vertical axis represents the output value from the CIS 202. Thepredetermined times α, β, and γ indicated along the horizontal axis aremeasured by the timer 31 d. The sheet S is first conveyed by theconveyance roller portion 201 (conveyance-roller-pair conveyance period,see Step S3), and then is conveyed by the obliquely-conveying rollerportion 205 (obliquely-conveying-roller-pair conveyance period, see StepS7). As the sheet S is conveyed by the obliquely-conveying rollerportion 205, the position (hereinafter referred to as a detectionposition) of the side edge portion Sa detected by the CIS 202 graduallyapproaches the position (hereinafter referred to as a referenceposition) of the reference surface 204 a of the reference member 204 inthe width direction W.

If the detection position is within the predetermined range L when thepredetermined time β has elapsed since the conveyance sensor 203detected the leading edge Sb of the sheet S, the controller 31 continuesto perform the normal control. Since the normal control is continued,the side edge portion Sa of the sheet S abuts against the referencesurface 204 a and the oblique conveyance is completed before thepre-registration sensor 206 detects the leading edge Sb of the sheet S.When the oblique conveyance is completed, the oblique-conveyance periodends. After that, the sheet S is conveyed while the side edge portion Saof the sheet S slides on the reference surface 204 a, so that thedetection position is kept at the reference position (reference-memberslide-and-conveyance period).

When the predetermined time γ has elapsed since the pre-registrationsensor 206 detected the leading edge Sb of the sheet S, the controller31 causes the obliquely-conveying roller portion 205 to end theconveyance of the sheet S (that is, the obliquely-conveying-roller-pairconveyance period ends). Then the controller 31 causes the registrationroller pair 207 to start the conveyance of the sheet S (that is, theregistration-roller-pair conveyance period starts).

FIG. 12 is a graph illustrating the output value from the CIS 202 thatchanges with time, and that is obtained when the recovery control isperformed by the controller 31. The horizontal axis represents the time,and the vertical axis represents the output value from the CIS 202. Thesheet S is first conveyed by the conveyance roller portion 201(conveyance-roller-pair conveyance period, see Step S3), and then isconveyed by the obliquely-conveying roller portion 205(oblique-conveyance period, see Step S7). As the sheet S is conveyed bythe obliquely-conveying roller portion 205, the position (hereinafterreferred to as a detection position) of the side edge portion Sadetected by the CIS 202 gradually approaches the position (hereinafterreferred to as a reference position) of the reference surface 204 a ofthe reference member 204 in the width direction W.

If the detection position is out of the predetermined range L when thepredetermined time β has elapsed since the conveyance sensor 203detected the leading edge Sb of the sheet S (Step S9: No), thecontroller 31 executes the recovery control. In the recovery control,the controller 31 increases the rotational speed of theobliquely-conveying roller portion 205 (see Step S10). Since therecovery control is executed, the speed at which the detection positionapproaches the reference position increases, and the side edge portionSa abuts against the reference surface 204 a and the oblique conveyanceis completed before the pre-registration sensor 206 detects the leadingedge Sb of the sheet S. After that, the sheet S is conveyed while theside edge portion Sa of the sheet S slides on the reference surface 204a, so that the detection position is kept at the reference position(reference-member slide-and-conveyance period).

When the predetermined time γ has elapsed since the pre-registrationsensor 206 detected the leading edge Sb of the sheet S, the controller31 causes the obliquely-conveying roller portion 205 to end theconveyance of the sheet S (that is, the obliquely-conveying-roller-pairconveyance period ends). Then the controller 31 causes the registrationroller pair 207 to start the conveyance of the sheet S (that is, theregistration-roller-pair conveyance period starts). Summary of FirstEmbodiment

As described above, in the abutment operation in which the sheet S isabutted against the reference surface 204 a by the obliquely-conveyingroller portion 205, the registration unit 144 of the first embodiment iscontrolled such that the conveyance force of the obliquely-conveyingroller portion 205 is controlled at the first conveyance force until thepredetermined time β has elapsed. In addition, if the predetermined timeβ has elapsed, and the position of the side edge portion Sa detected bythe CIS 202 is out of the predetermined range L, the registration unit144 is controlled such that the conveyance force of theobliquely-conveying roller portion 205 is controlled at the secondconveyance force larger than the first conveyance force, by increasingthe rotational speed of the obliquely-conveying roller portion 205. As aresult, even if the sheet S has a large conveyance resistance and theconveyance delay occurs in the skew correction of the sheet S, theregistration unit 144 can quickly complete the abutment operation andprevent the productivity from being lowered in the skew correction ofthe sheet S.

Second Embodiment

Next, a registration unit 144 of a second embodiment will be described.The registration unit 144 of the second embodiment changes theconveyance force of the obliquely-conveying roller portion 205 in therecovery control, by increasing the nip pressure of theobliquely-conveying roller portion 205, without changing the rotationalspeed of the obliquely-conveying roller portion 205. The registrationunit 144 of the second embodiment differs from the registration unit 144of the above-described first embodiment in this point. Since the otherconfiguration of the second embodiment is the same as that of the firstembodiment, a component identical to that of the first embodiment isgiven an identical symbol, a process identical to that of the firstembodiment is given an identical step number, and the descriptionthereof will be omitted.

With reference to a flowchart of FIG. 13 , an abutment operation of theregistration unit 144 of the second embodiment, in which the sheet S isabutted against the reference surface 204 a, will be described. If thecontroller 31 determines that the predetermined time α has elapsed sincethe conveyance sensor 203 detected the leading edge Sb of the sheet S(S4 Yes), then the controller 31 determines that the sheet S has beenconveyed to the obliquely-conveying roller portion 205 by the conveyanceroller portion 201. Then the controller 31 causes theobliquely-conveying attachment-and-detachment units 35 a to 35 c, whichserves as a nip-pressure adjustment portion, to switch the state of theobliquely-conveying roller portion 205 to a weak nip state (S21). In theweak nip state, the nip pressure of the obliquely-conveying rollerportion 205 is controlled at a first pressure.

In the registration unit 144, in the steps S6, S7, and S21, the obliqueconveyance of the sheet S is started by the obliquely-conveying rollerportion 205, and the skew of the sheet S and the position of the sheet Sin the width direction W are corrected as the sheet is conveyedobliquely. In addition, in the steps S7 and S21, the controller 31controls the obliquely-conveying roller portion 205 so that therotational speed and the nip pressure of the obliquely-conveying rollerportion 205 are controlled at a first rotational speed and a firstpressure, which are preset for each type of the sheet S. Thus, thecontroller 31 controls the conveyance force of the obliquely-conveyingroller portion 205 at a first conveyance force, and causes theobliquely-conveying roller portion 205 to convey the sheet S.

If the controller 31 determines in Step S9 that the position of the sideedge portion Sa of the sheet S is not within the predetermined range Lat the position of the CIS 202 (S9 No), then the controller 31determines that the sheet S has a large conveyance resistance and isbeing conveyed with delay. In this case, since the conveyance delay ofthe sheet S is not eliminated even if the normal control is continued,the controller 31 executes recovery control and changes the conveyanceforce of the obliquely-conveying roller portion 205, for eliminating theconveyance delay. In the recovery control, the controller 31 of thesecond embodiment increases the conveyance speed of the sheet S byswitching the state of the obliquely-conveying roller portion 205 to astrong nip state, by causing the obliquely-conveyingattachment-and-detachment units 35 a to 35 c to increase the nippressure of the obliquely-conveying roller portion 205 from the firstpressure to a second pressure higher than the first pressure (S22).

In this manner, the controller 31 changes the conveyance force of theobliquely-conveying roller portion 205 to a second conveyance forcelarger than the first conveyance force, which is set in the steps S7 andS21. As a result, the sheet S can be conveyed downstream in the sheetconveyance direction C, without conveyance delay.

As described above, in the abutment operation of the obliquely-conveyingroller portion 205 in which the sheet S is abutted against the referencesurface 204 a, the registration unit 144 of the second embodiment iscontrolled such that the conveyance force of the obliquely-conveyingroller portion 205 is controlled at the first conveyance force until thepredetermined time β has elapsed. In addition, if the predetermined timeβ has elapsed, and the position of the side edge portion Sa detected bythe CIS 202 is out of the predetermined range L, the registration unit144 is controlled such that the conveyance force of theobliquely-conveying roller portion 205 is controlled at the secondconveyance force larger than the first conveyance force, by increasingthe nip pressure of the obliquely-conveying roller portion 205. As aresult, even if the sheet S has a large conveyance resistance and theconveyance delay occurs in the skew correction of the sheet S, theregistration unit 144 can quickly complete the abutment operation andprevent the productivity from being lowered in the skew correction ofthe sheet S.

Third Embodiment

Next, a registration unit 144 of a third embodiment will be described.The registration unit 144 of the third embodiment changes the conveyanceforce of the obliquely-conveying roller portion 205 in the recoverycontrol, by increasing the rotational speed and the nip pressure of theobliquely-conveying roller portion 205. The registration unit 144 of thethird embodiment differs from the registration unit 144 of theabove-described first embodiment and the registration unit 144 of theabove-described second embodiment in this point. Since the otherconfiguration of the third embodiment is the same as that of the firstand the second embodiments, a component identical to that of the firstand the second embodiments is given an identical symbol, a processidentical to that of the first and the second embodiments is given anidentical step number, and the description thereof will be omitted.

With reference to a flowchart of FIG. 14 , an abutment operation of theregistration unit 144 of the third embodiment, in which the sheet S isabutted against the reference surface 204 a, will be described. If thecontroller 31 determines in Step S9 that the position of the side edgeportion Sa of the sheet S is not within the predetermined range L at theposition of the CIS 202 (S9 No), then the controller 31 determines thatthe sheet S has a large conveyance resistance and is being conveyed withdelay. In this case, since the conveyance delay of the sheet S is noteliminated even if the normal control is continued, the controller 31executes recovery control and changes the conveyance force of theobliquely-conveying roller portion 205, for eliminating the conveyancedelay.

In the recovery control, the controller 31 of the third embodimentincreases the rotational speed of the obliquely-conveying roller portion205 from the first rotational speed to the second rotational speed, byincreasing the rotational speed of the obliquely-conveying drivingmotors 34 a to 34 c. In addition, in the recovery control, thecontroller 31 switches the state of the obliquely-conveying rollerportion 205 to the strong nip state, by causing the obliquely-conveyingattachment-and-detachment units 35 a to 35 c to increase the nippressure of the obliquely-conveying roller portion 205 from the firstpressure to the second pressure higher than the first pressure. That is,the controller 31 increases the conveyance speed of the sheet S byincreasing the rotational speed and the nip pressure of theobliquely-conveying roller portion 205 (S31).

In this manner, the controller 31 changes the conveyance force of theobliquely-conveying roller portion 205 to the second conveyance forcelarger than the first conveyance force, which is set in the steps S7 andS21. As a result, the sheet S can be conveyed downstream in the sheetconveyance direction C, without conveyance delay.

As described above, in the abutment operation in which the sheet S isabutted against the reference surface 204 a by the obliquely-conveyingroller portion 205, the registration unit 144 of the third embodiment iscontrolled such that the conveyance force of the obliquely-conveyingroller portion 205 is controlled at the first conveyance force until thepredetermined time β has elapsed. In addition, in the registration unit144, if the predetermined time β has elapsed, and the position of theside edge portion Sa detected by the CIS 202 is out of the predeterminedrange L, the rotational speed and the nip pressure of theobliquely-conveying roller portion 205 are increased. In this manner, inthe registration unit 144, the conveyance force is controlled at thesecond conveyance force larger than the first conveyance force. As aresult, even if the sheet S has a large conveyance resistance and theconveyance delay occurs in the skew correction of the sheet S, theregistration unit 144 can quickly complete the abutment operation andprevent the productivity from being lowered in the skew correction ofthe sheet S. Modifications

Note that in the first to the third embodiments, the conveyance of thesheet S is stopped if the abutment operation of the sheet S is notcompleted before the leading edge Sb of the sheet S reaches theregistration roller pair 207. However, the present disclosure is notlimited to this. For example, if the abutment operation of the sheet Sis not completed before the leading edge Sb of the sheet S reaches theregistration roller pair 207, the controller 31 may cause the switchingmotor 37 to drive the guide member 151. In this case, the sheet S may bedischarged to the escape tray 152 through the escape path 151 a.

In this configuration, even if the abutment operation is not completedbefore the leading edge Sb of the sheet S reaches the registrationroller pair 207, the registration unit 144 does not stop the conveyanceof the sheet S, and thus can prevent the productivity from beinglowered. In addition, a user of the printer 1 can distinguish a sheethaving a defect in printing, caused by the uncompleted abutmentoperation, from sheets discharged to the discharging tray 148; and caneasily remove the sheet discharged to the escape tray 152. Thus, theusability can be increased.

In addition, although the registration unit 144 causes theobliquely-conveying attachment-and-detachment units 35 a to 35 c tobring the driven rollers into contact with the driving rollers andseparate the driven rollers from the driving rollers in the first to thethird embodiments, the present disclosure is not limited to this. Forexample, the registration unit 144 may cause the obliquely-conveyingattachment-and-detachment units 35 a to 35 c to bring the drivingrollers into contact with the driven rollers and separate the drivingrollers from the driven rollers.

In addition, in the first to the third embodiments, the predeterminedrange L is, for example, ±0.3 mm with respect to the position of thereference surface 204 a in the width direction W. However, the presentdisclosure is not limited to this. The predetermined range L may be setin advance, as appropriate, in accordance with desired print precisionor a sheet size, or may be set by a user.

In addition, in the first to the third embodiments, the controller 31determines whether the position of the side edge portion Sa of the sheetS is within the predetermined range L at the position of the CIS 202,when the predetermined time β has elapsed since the conveyance sensor203 detected the leading edge Sb of the sheet S. However, the operationof the controller 31 is not limited to this. For example, the controller31 may cause the timer 31 d to start to measure time when the conveyanceof the sheet S is started by the obliquely-conveying roller portion 205.In this case, when a predetermined time has elapsed since the conveyanceof the sheet S was started by the obliquely-conveying roller portion 205and the timer 31 d started to measure time, the controller 31 maydetermine whether the position of the side edge portion Sa of the sheetS is within the predetermined range L at the position of the CIS 202.

In addition, in the first to the third embodiments, theobliquely-conveying roller portion 205 is disposed in front of thesecondary transfer nip T2. However, the present disclosure is notlimited to this. For example, the obliquely-conveying roller portion 205may be disposed in the duplex conveyance unit 149 or another apparatuslocated downstream of the printer 1 and connected to the printer 1, andthe present invention may be applied to such a configuration.

In addition, in the first to the third embodiments, the conveyanceroller portion 201 includes the three conveyance roller pairs, and theobliquely-conveying roller portion 205 includes the threeobliquely-conveying roller pairs. However, the number of the rollerpairs is not limited to a particular number. In addition, theobliquely-conveying roller pairs 205 a to 205 c are inclined by theidentical angle of θ with respect to the sheet conveyance direction C.However, the present disclosure is not limited to this. For example, theobliquely-conveying roller pairs 205 a to 205 c may be inclined bydifferent angles with respect to the sheet conveyance direction C.

In addition, in the first to the third embodiments, the presentinvention has been described, for example, for the registration unit144, which serves as a sheet conveyance apparatus that includes thecontroller 31. However, the printer 1 may be regarded as a sheetconveyance apparatus.

In addition, in the first to the third embodiments, the description hasbeen made for the electrophotographic printer 1. However, the presentinvention is not limited to this. For example, the present invention mayalso be applied to an ink-jet image forming apparatus that forms imageson sheets by injecting ink from a nozzle.

The present invention may be embodied by providing a program, whichachieves one or more functions of the above-described embodiments, to asystem or an apparatus via a network or a storage medium, and by causingone or more processors of the system or the apparatus to read andexecute the program. In addition, the present invention may be embodiedby a circuit (for example, an ASIC) that achieves one or more functions.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2021-174829, filed Oct. 26, 2021, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A sheet conveyance apparatus comprising: aconveyance roller configured to convey a sheet; an abutment memberincluding an abutment surface and configured to correct skew of thesheet, the abutment surface being disposed downstream of the conveyanceroller and extending along a sheet conveyance direction, the abutmentsurface being a surface against which a side edge portion of the sheetin a width direction orthogonal to the sheet conveyance direction abuts;an obliquely conveying roller disposed downstream of the conveyanceroller in the sheet conveyance direction and configured to convey thesheet such that the side edge portion is moved toward the abutmentsurface; a sheet side-edge detection portion configured to detect aposition of the side edge portion of the sheet in the width directionand change an output value in accordance with the position of the sideedge portion of the sheet conveyed by the obliquely conveying roller;and a controller configured to control conveyance force applied by theobliquely conveying roller in the width direction of the sheet, inaccordance with a detection result from the sheet side-edge detectionportion, wherein the controller is configured to control the conveyanceforce of the obliquely conveying roller at a first conveyance forceuntil a predetermined time has elapsed, in an abutment operation inwhich the sheet is abutted against the abutment surface by the obliquelyconveying roller, and control the conveyance force of the obliquelyconveying roller at a second conveyance force larger than the firstconveyance force if the predetermined time has elapsed and the positionof the side edge portion of the sheet detected by the sheet side-edgedetection portion is out of a predetermined range.
 2. The sheetconveyance apparatus according to claim 1, wherein the controller isconfigured to control rotational speed of the obliquely conveying rollerat a first rotational speed if the conveyance force of the obliquelyconveying roller is controlled at the first conveyance force, andcontrol the rotational speed of the obliquely conveying roller at asecond rotational speed faster than the first rotational speed if theconveyance force of the obliquely conveying roller is controlled at thesecond conveyance force.
 3. The sheet conveyance apparatus according toclaim 1, wherein the obliquely conveying roller includes a drivingroller configured to rotate, and a driven roller, the driving rollerbeing configured to drive the driven roller, the driving roller and thedriven roller being configured to form a nip and convey a sheet whilenipping the sheet in the nip, wherein the controller is configured tocontrol nip pressure of the nip at a first pressure if the conveyanceforce of the obliquely conveying roller is controlled at the firstconveyance force, and control the nip pressure of the nip at a secondpressure higher than the first pressure if the conveyance force of theobliquely conveying roller is controlled at the second conveyance force.4. The sheet conveyance apparatus according to claim 1, wherein if thepredetermined time has elapsed and the position of the side edge portionof the sheet detected by the sheet side-edge detection portion is withinthe predetermined range, the controller controls the conveyance force ofthe obliquely conveying roller at the first conveyance force until theabutment operation is completed.
 5. The sheet conveyance apparatusaccording to claim 1, wherein the predetermined time is a first time,wherein the conveyance roller is a first conveyance roller, wherein thesheet conveyance apparatus further includes a sheet downstream-edgedetection portion disposed downstream of the obliquely conveying rollerin the sheet conveyance direction and configured to detect an edgeportion of the sheet on a downstream side in the sheet conveyancedirection, and a second conveyance roller disposed downstream of thesheet downstream-edge detection portion in the sheet conveyancedirection and configured to convey the sheet, and wherein the controlleris configured to cause the second conveyance roller to convey the sheetif a second time has elapsed since the sheet downstream-edge detectionportion detected the edge portion of the sheet on the downstream side.6. The sheet conveyance apparatus according to claim 5, wherein thecontroller is configured to separate the obliquely conveying roller fromthe sheet when the controller causes the second conveyance roller toconvey the sheet.
 7. The sheet conveyance apparatus according to claim6, wherein the obliquely conveying roller further includes a drivingroller configured to rotate, and a driven roller, the driving rollerbeing configured to drive the driven roller, the driving roller and thedriven roller being configured to form a nip and convey a sheet whilenipping the sheet in the nip, and wherein the controller is configuredto remove the nip by separating the driven roller from the drivingroller when the controller causes the second conveyance roller to conveythe sheet.
 8. The sheet conveyance apparatus according to claim 5,wherein in a period of time from when the abutment operation is starteduntil when the sheet downstream-edge detection portion detects the edgeportion of the sheet on the downstream side, if the position of the sideedge portion of the sheet detected by the sheet side-edge detectionportion is within the predetermined range, the controller determinesthat the abutment operation has been completed.
 9. The sheet conveyanceapparatus according to claim 8, further comprising: a first tray towhich a sheet is discharged; and a second tray to which a sheet isdischarged and which is different from the first tray, wherein a sheeton which the controller has determined that the abutment operation hasbeen completed is discharged to the first tray, and wherein a sheet thathas reached the second conveyance roller in a state where the controllerhas determined that the abutment operation has not been completed on thesheet is discharged to the second tray.
 10. The sheet conveyanceapparatus according to claim 1, further comprising an image formingportion configured to form an image on a sheet.